Back in April staff were told that a deal to sell the refinery to investment firm Greybull Capital had fallen through and management had entered a period of consultation over its future.

The refinery, which is owned by Murphy Oil Corporation and employs around 400 people, has been on the market for about three years.

Mr Crabb told the Western Telegraph: "This is a crucial week for the refinery. There is a very active sales process in play with one potential buyer and negotiations seem to be coming to a head. But, as we have seen before, there can be no certainty in a challenging commercial matter.

“Both UK and Welsh governments are engaged at the highest level to do what they can to help achieve a successful outcome, but the buyer must ultimately be in a position to make an acceptable offer to Murphy."

Mr Crabb said he was in close contact with Welsh and UK government ministers, as well as both the buyer and Murphy.

“Hundreds of good quality jobs depend on a successful sale and I remain determined to do everything I possibly can as local MP to see that refinery stay open," he added, but was unable to disclose who the potential buyer is.